Life's Origins at Four Billion Years Ago; Implications for Our Future

A group from the University of Tokyo (Tashiro et al, 2017) argues in a Nature paper that carbon isotope ratios in rocks in northern Labrador, Canada means that those rocks harbored life almost four billion years ago. This pushes back the early bound on origin of life almost two hundred million years, almost to the Hadean eon. To be sure this finding has not been universally accepted, but it's worth thinking about what it would mean. In particular, and perhaps not coincidentally, this is also right about when the Earth's surface transitioned from molten to solid. [Added later: it turns out the Moon may have been briefly "habitable", i.e. had an atmosphere and liquid water. Look for the same signature in rocks there?]

A recent paper reconstructing the last universal common ancestor (LUCA's) genome from a massive tree of millions of genes showed that it was pretty clearly a sulfur-vent organism. This is good news if you're looking for life on Europa or Enceladus, because that means that life on Earth didn't need the sun (and neither would any life that could evolve along vents under Europa's icy crust.) If you assume that the chance of life evolving by 3.5 billion years ago on Earth was 50%, and that the chance of life evolving is based on surface area, and all other things are equal (admittedly speculative when we don't even have all the information for our N=1) then there is a one in three chance of life on Europa. (If that probability correlates instead with the volume of water, then it was overwhelmingly more likely for life to evolve on Europa!)

[Added several days later: someone has finally run the numbers. A model of RNA polymer formation by Pearce et al suggests that the first RNA world molecules were most likely to have formed in small surface pools rather than sulfur vents - but even earlier, 4.17 billion years ago. If a wet-dry cycle is needed, this suggests ocean worlds like Europa are less likely than once-wet places with exposed land like Mars. The lesson of this paper is that you need puddles, not bone-dry deserts or world-spanning oceans. In this model, a world with puddles and organics seems all but certain to develop into an RNA world. A paper by Cardenas et al from the Geological Society of America Bulletin strongly suggests that 3.5 billion years ago, Mars was exactly the kind of place to have puddles. The logical argument is that life, or at least an RNA world, also developed very quickly there, and we should look for similar deposits to the ones found by Tashiro et al. If Pearce's argument does not produce findings like Tashiro's on Mars, we at least can start looking for differences in the early environments of the two.]

Two things to keep in mind about the LUCA paper: 1) LUCA is the last universal common ancestor. There could be a long lineage before it; and 2) the smaller and simpler a system, the more profound the changes possible in that system. If at one point Earth was an RNA World, molecular clock techniques developed based on modern DNA metabolism would probably be pretty bad at retrodicting LUCA. That two hundred million year gap map be exactly that. All that carbon might be free-floating ribosomes, or peri-biotic viroids.

Even more importantly, this has implications for the likelihood of the evolution of life. This discovery should worry you if you consider the Great Filter. The idea is that it seems very likely that life would evolve anywhere there's liquid water. Yet the universe is not obviously filled with intelligent life. Something is therefore stopping the progression from the evolution of life, to that life spreading from its home planet. (This is typically assumed to be some natural event and need not be some science fiction plot of an alien menace stamping out intelligence wherever it appears.) And every time that the origin of life is pushed back a bit further - that gives greater cause to worry, because where probabilistic events are concerned, the faster something happened, the more likely it was. If this paper is correct, then life on Earth appeared essentially as soon as the surface cooled from magma to solid. [Added several days later:

The real question is whether the Great Filter is behind us (we're freaks that got more complicated than algae) or in front of us (every intelligence is powerful but short-sighted and wrecks its own ecology before it can escape its home planet.) Therefore, a very reassuring discovery would be simple life - the local flavor of blue-green algae - under the ice Europa of Enceladus,* and in the ancient mud of dried Martian riverbeds, and baked into Venusian bedrock. That would mean that somehow, we got past the gate - still no guarantees, but we already passed the filter. This would mean that if we do manage to get out of the solar system, we'll find a lot of alien bacterial mats, but no alien minds. Boring? That idea is actually quite reassuring.

On the other hand, a bad discovery would be mass fossil beds of complex multicellular things (like the radioactive squid in Europa Report), especially ones with extrasomatic adaptations (tools.) We have had a number of landers on Mars and Venus, and none of them captured any obvious macroscale life. But a positive finding by SETI would be even more harrowing, especially because it's unlikely that there would be only one other intelligence that happens to be even within a million years of our technology - even if they're within 1% as old as we are, that's a gap of 40 million years in either direction! In such a situation we would have to include they must be legion. In such a situation, we would have to reason: we can hear them, but for some reason they never get away from their home planet - and we are unlikely to be any different.

*If indeed we believe that Enceladus only formed in the Cretaceous, then there is much less likely to be life there than Europa, and we should focus on Europa.

Previous post about alien evolution, Vast Cool and Unsympathetic: Other Worlds Detecting Earth


REFERENCES
Benjamin T. Cardenas, David Mohrig, Timothy A. Goudge. Fluvial stratigraphy of valley fills at Aeolis Dorsa, Mars: Evidence for base-level fluctuations controlled by a downstream water body. GSA Bulletin, 2017; DOI: 10.1130/B31567.1

Pearce BKD, Pudritz RE, Semenov DA, Henning TK. Origin of the RNA world: The fate of nucleobases in warm little ponds. 10.1073/pnas.1710339114 PNAS October 2, 2017

Tashiro T, Ishida A, Masako Hori M, Motoko Igisu M, Mizuho Koike M, Pauline Méjean P, Naoto Takahata N, Yuji Sano Y, Komiya T. Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada. Nature 549, 516–518 (28 September 2017) doi:10.1038/nature24019

We Are Living in a Simulation: Specifically, Minecraft

[Welcome BoingBoing deviants. You want metal? You want aliens and simulation arguments and singularity stuff? We got all that. Check us out for a while. - Mike]

Forget self-indication assumptions that favor Bostrom's simulation argument. You don't need them. Some parts of the planet don't even bother to conceal the original Minecraft geometry.


From Strange Interesting Facts.


I mean come on. When you see unfinished work like that sitting around, you realize there's no point in worrying whether the Simulators would get mad if we forced them to use more bandwidth by making higher resolution models of the universe. They clearly don't care if we figure it out. This is Roraima Mountain, a tepuy (table mountain of Precambrian basement rock) that lies on the triple point between Venezuela, Brazil and Guyana. Read this for an account of the isolated top, scrubbed of nutrients by time and rain: "Contrary to our expectations the top was far from flat, with strange shapes eroded by both wind and water forming peaks and troughs..." (Non-Euclidean shapes?) The poor nutrition of the rock and "soil" favors carnivorous plants, and some reproductively isolated black frogs scamper on four legs like lizards. Check out the pictures at that link; the flora and geology at the top looks like a little transplanted South Utah in the middle of the jungle.

Where Are the Post-Singularity Replicators: A New One for Fermi and Bostrom

One of the underlying assumptions of singularity arguments is that not only will technology improve sufficiently to hit an inflection point beyond which tools improve themselves to the point of something usefully called intelligence and reproduction, but that this is basically inevitable, as long as we don't destroy ourselves before then. (Whether the singularity would destroy us is another question.) A final assumption is that sufficiently advanced post-singularity machines will be able to preserve or add to themselves, or replicate, by recruiting "dumb" matter far better than current Earth biology can, as we do when we eat and breathe.

If we make the additional assumption that any intelligence in the universe which uses tools and has behavior will incrementally improve those tools - then the same should happen for any other species.

Taking these assumptions as valid, we should assume that the universe we observe should already be heavily influenced by singularity events. But it is NOT obviously behaving in any way that dumb matter doesn't behave. I observed in a previous post that singularity arguments, taken to their conclusion, track Bostrom and Fermi: if these are such powerful principles in the evolution of the universe, shouldn't we already be experiencing the consequences?

Even more generally speaking (outside of singularity arguments) shouldn't we assume that, given enough time, most matter and energy will eventually be locked up into replicators, if living things and/or intelligence continues to expand? It's worth emphasizing that all of the arguments are some version of the self-indication argument, although the where-are-all-the-singularity argument is a hypothetical SIA, which I am using to argue against the probability of a singularity.

The most likely answer, based on what we know so far, is that there have been no singularities, which in turn means that it is less likely than we might otherwise have thought that we will have a singularity. While some version of panspermia seems more and more plausible, the seeding of young worlds with nucleobases and amino acids isn't exactly what people have in mind in these discussions. Indeed the absence of expanding "life clouds" argues not just against singularities as such but against the indefinite expansion and survival of life. But there are a number of possible counterarguments:

- Entropy wins; matter and energy also get locked up into black holes faster than life and/or intelligence can employ that matter for their own preservation.

- By the nature of physics, only a very small fraction of matter and energy can be pressed into service as a substrate for life and intelligence.

- Replicators are always unstable processes. This solves Fermi's paradox by making Drake's omega attrition factor much more influential to the outcome.

- Most of what we observe is indeed the result of such processes (galaxies, stars, our own solar system?) and we either don't have the pattern recognition skills to see it or are only observing a vanishingly small slice of possible data. (This one makes for the best science fiction ideas, and also is more analogous to Bostrom than Fermi.)

- Humans are the only species that uses tools and improves them.

- We're lucky and we're the first, or one of the first, and the expanding sphere of others' computronium hasn't hit us yet.

If I had to bet, I would bet against the last two.

The Great Filter: Why All This Talk of "Civilizations?"

In discussions of filters and Fermi paradoxes, questions are often asked with the word "civilization". Why, we wonder, do we not see evidence of non-human civilizations?

The concern for the absence of evidence of civilizations has been that it is probably unreasonable to assume that humans are special (the self-indication assumption), and that, since the evolution of life elsewhere in the galaxy seems more and more likely (more planets discovered, more ways of making heredity chemicals), it's worrisome that we don't see evidence of other civilizations. Why worrisome? Because it may mean that the "filter" that stops civilizations from filling the sky seems less and less likely to be between the primordial chemical soup of young planets and the evolution of living things, and therefore more and more likely to be after the evolution of life and their surviving long enough to colonize the galaxy. That is to say, whatever it is which seems to have consistently stopped the others' expansion is probably still ahead of us in time. By this argument, any observation which makes it more likely on average for planets to get at least as far as humans are on the way to intelligence and interstellar diaspora is bad news, because it means the filter must still be in front of us.

There are two assumptions here which, if falsified, break the logic of these arguments. One is that the sky really is empty. We've only just started looking and it's not at all clear we know what to look for, or where (related posts here.) Second is that at this point it is totally
unwarranted to insist that matter-based replicators which move between stars must necessarily have, or be the product of, a "civilization". The provinciality of such an assumption cannot be over-stated. Certainly with most Earth organisms, there is no conceivable way to move between star systems without a specialized representational tissue that allows behavior-changing information to be cooperatively shared by large numbers of entities. This is what we call "civilization" in the one species that we know has developed it. But if it is indeed possible for non-intelligent replicators to spread between stars (even if slowly; see calculations here) there's still a good chance we'll find it. If it's possible for non-intelligent life to spread, and we don't find it, there's a good chance that the filter is in fact the evolution of life in the first place (despite all mounting findings apparently to the contrary), not the stability or longevity of "civilizations" that would otherwise be thought necessary to help intelligences escape the quarantines of their solar systems. In that case, we're out of the woods, and we're on our own.